1. Field of the Invention
The present invention relates to an access sheath for endoluminally accessing a body cavity and directing the passage of interventional devices therethrough into the cavity. Particularly, the present invention relates to an articulatable access sheath which directs the interventional devices into the cavity in a desired orientation. In some embodiments, the present invention relates to vascularly accessing an atrium of the heart to direct an interventional catheter toward a cardiac valve.
To access a target location within the human body from a remote location, a catheter is typically passed through one or more body lumens, such as through the vascular system, to the target location. When the vascular system is used, a guidewire and dilator is inserted into an artery or vein through a relatively small incision in the patient's body. The guidewire and dilator is then threaded through the patient's vasculature to reach the desired target area. Often the dilator is covered by a sheath which is passed with the dilator to the target location. The dilator is then removed and the sheath is used as a conduit for access for a variety of medical devices to access the target location. Such devices may include catheters, surgical instruments, fiber optic cables for visualization, lasers, electronic devices, or sensors capable of monitoring physiological parameters in situ, to name a few. Although such access reduces the need for traditional invasive surgery, challenges arise related to control, manipulation, and positioning of instruments near the target location, particularly within a target body cavity.
A device advanced to the cavity will typically protrude into the cavity at the angle in which it entered. If the target tissue is not within this pathway, the device will need to be steered toward the target tissue. If more than one device is used during a procedure, each device will need to be steered and repositioned when used. This increases the time and cost of the procedure and also the risk of misalignment.
For example, to gain access to the left atrium of the heart, the catheter and/or access sheath may be tracked from a puncture in the femoral vein, through the inferior vena cava, into the right atrium and through a puncture in the intra-atrial septum to the left atrium. This pathway may then be used to access the mitral valve which lies between the left atrium and the left ventricle. From the point of entry through the septum, the mitral valve may be located below and to the right or left requiring the devices which are inserted to be directed downward and perhaps laterally after entry, toward the mitral valve. In addition, devices used for applying interventional therapies to the mitral valve may require precise alignment with the valve commissures, leaflets, or coaptation line to perform the procedure. When such procedures require the use of more than one instrument, each instrument would be dependent upon proper positioning in relation to the valve. This would require that positioning or steering mechanisms be built into each instrument and each instrument would be required to be properly positioned when introduced. This adds cost, complexity, and time to the overall procedure.
To overcome some of these challenges, access sheaths have been developed to direct instruments that are passed therethrough. For example, an access sheath having a pre-shaped curve at its distal end has been developed to both assist in negotiating twists and branches common in a patient's arterial or venous system and to maintain a shape once positioned within a target cavity. Since the pre-shaped curve is fixed into the access sheath at the time of manufacture, the radius and extent of the curvature generally cannot be altered. Due to anatomical variations, extensive pre-surgical planning would be necessary to determine the correct curvature of the access sheath. Such tailoring would be prohibitively complex and a predicted curvature would most likely still require additional repositioning once inside the body. Continuously replacing the pre-shaped access catheter in hopes of obtaining the proper curvature would be expensive and time consuming, possibly placing the patient at additional risk.
Steerable guide catheters and delivery catheters have been developed to more effectively navigate through the tortuous pathways of some body lumens, particularly the vascular system. Typically steering is accomplished through a combination of torqueing the proximal end of the catheter and pulling various pullwires to deflect the distal end of the catheter. Unfortunately, torque transmission has not been perfected in such steerable catheters. Due to the length of the catheter body between a proximal control end and the distal tip, torsion can tend to accumulate as the proximal end of the catheter is twisted to rotate the tip. The accumulated torsional moment may release unevenly, resulting in skipping or rapid rotation of the distal tip inside the vessel. To optimize torque transmission, the walls of such steerable catheters generally comprise a series of layers. In a typical steerable catheter, a woven metal or polymeric tubular braid may be sandwiched between an inner tubular sleeve and an outer tubular jacket. As a consequence, improved torquability generally results in increased wall thickness, which in turn increases the outside diameter of the steerable catheter or reduces any given desired inside diameter. In addition, such a heavy braided construction is often difficult to deflect by actuation of pullwires. To overcome this, the deflectable section can be softened with coils or softer polymers to allow it to be deflected to a much greater extent. However, this reduces the catheter's ability to transmit torque to or through this softer section. In addition, these softer sections may not offer adequate support for interventional devices or tools which are later passed through its inner lumen.
For these reasons, it would be desirable to provide an access sheath having an articulatable distal end which does not rely on permanent pre-shaping or torque transmission for positioning the access sheath within a target body cavity in a desired orientation. The articulatable access sheath should have a large lumen diameter to accommodate the passage of a variety of interventional devices, should have good wall strength to avoid kinking or collapse of the sheath when bent around tight curves, and should have good column and tensile strength to avoid deformation when the interventional devices are passed through the lumen. The sheath articulation mechanisms should provide for a high degree of controlled deflection at the distal end of the sheath but should not take up significant lumen area to allow for passage of interventional devices. Further, the access sheath should be articulatable in a manner which allows compound curves to be formed, for example curvature within more than one plane. Such manipulation should allow fine control over the distal end to accommodate anatomical variations within the same type of body cavity and for use in different types of body cavities.
2. Description of the Background Art
Hermann et al. (U.S. Pat. No. 5,843,031) describes a large-diameter introducer sheath having a hemostasis valve and a removable steering mechanism. The steering mechanism is described to be within an obturator which is positioned within the sheath during positioning and is then removable. Adair (U.S. Pat. No. 5,325,845) describes a steerable sheath having an articulatable member which is deformable to allow articulation. Kordis (U.S. Pat. No. 5,636,634) describes a sheath which is positioned by a separate, dedicated steering catheter.
A number of the other references refer to guidewires or catheters which themselves are steerable by means of wires. For example, Stevens-Wright et al. (U.S. Pat. No. 5,462,527) describes a handle which applies tension selectively to two or four pull cables to steer an attached catheter. Stevens-Wright et al. (U.S. Pat. No. 5,715,817) further describes improvements in actuating the tip of the catheter described in Stevens-Wright et al. '527.
Hammerslag (U.S. Pat. No. 5,108,368) describes a steerable guidewire or catheter wherein the tip is deflectable through a full 360 degree range of motion by means of axially moveable deflection wires extending throughout. Hammerslag (U.S. Pat. No. 5,820,592) describes a guide catheter through which a torque control wire or a deflection wire extends. Manipulating an actuator controls the wire to steer or aim the guide catheter. Savage (U.S. Pat. No. 5,368,564) and Savage et al. (U.S. Pat. No. 5,507,725) also describe a steerable catheter having wire members extending through the catheter wall to manipulate the tip.
Likewise, the following also provide variations of the steerable catheters which utilize wires for manipulation: Accisano, III (U.S. Pat. No. 5,571,085), Krauter (U.S. Pat. No. 5,359,994), West et al. (U.S. Pat. No. 5,318,525), Nardeo (Pub. No. US 2001/0037084 A1), Bumbalough (U.S. Pat. No. 6,267,746), Webster, Jr. (U.S. Pat. No. 6,123,699), Lundquist et al. (U.S. Pat. No. 5,195,968) and Lundquist et al. (U.S. Pat. No. 6,033,378). Falwell et al. (U.S. Pat. No. 6,319,250) describes a catheter having any suitable steering mechanism known in the art.